Yes, it would be great, but I haven't found such a function, which
splits 2 dimensional array into rows =) Maybe we'll modify existing
function, but unfortunately we have tried hstore type and function in
postgres and we see a significant performance improvements. So we only
need to convert existing data into hstore and I think this is a good
solution.
On 12/14/2011 11:21 AM, Marc Mamin wrote:
Hello,
For such cases (see below), it would be nice to have an unnest function that only affect the first array dimension.
Something like
unnest(ARRAY[[1,2],[2,3]], SLICE=1)
=>
unnest
------
[1,2]
[2,3]
With this function, I imagine that following sql function
might beat the plpgsql FOREACH version.
CREATE OR REPLACE FUNCTION input_value_un (in_inputs numeric[], in_input_nr numeric)
RETURNS numeric AS
$BODY$
SELECT u[1][2]
FROM unnest($1, SLICE =1) u
WHERE u[1][1]=in_input_nr
LIMIT 1;
$BODY$
LANGUAGE sql IMMUTABLE;
best regards,
Marc Mamin
-----Original Message-----
From: pgsql-performance-owner@xxxxxxxxxxxxxx [mailto:pgsql-performance-
owner@xxxxxxxxxxxxxx] On Behalf Of Pavel Stehule
Sent: Dienstag, 13. Dezember 2011 15:43
To: Aleksej Trofimov
Cc: pgsql-performance@xxxxxxxxxxxxxx
Subject: Re: Postgres array parser
Hello
2011/12/13 Aleksej Trofimov<aleksej.trofimov@xxxxxxxxxx>:
We have tried foreach syntax, but we have noticed performance
degradation:
Function with for: 203ms
Function with foreach: ~250ms:
there is functions code:
CREATE OR REPLACE FUNCTION input_value_fe(in_inputs numeric[],
in_input_nr
numeric)
RETURNS numeric AS
$BODY$
declare i numeric[];
BEGIN
FOREACH i SLICE 1 IN ARRAY in_inputs
LOOP
if i[1] = in_input_nr then
return i[2];
end if;
END LOOP;
return null;
END;
$BODY$
LANGUAGE plpgsql VOLATILE
COST 100;
CREATE OR REPLACE FUNCTION input_value(in_inputs numeric[],
in_input_nr
numeric)
RETURNS numeric AS
$BODY$
declare
size int;
BEGIN
size = array_upper(in_inputs, 1);
IF size IS NOT NULL THEN
FOR i IN 1 .. size LOOP
if in_inputs[i][1] = in_input_nr then
return in_inputs[i][2];
end if;
END LOOP;
END IF;
return null;
END;
$BODY$
LANGUAGE plpgsql VOLATILE
COST 100;
On 12/13/2011 04:02 PM, Pavel Stehule wrote:
Hello
do you know FOREACH IN ARRAY statement in 9.1
this significantly accelerate iteration over array
http://www.depesz.com/index.php/2011/03/07/waiting-for-9-1-foreach-
in-array/
2011/12/13 Aleksej Trofimov<aleksej.trofimov@xxxxxxxxxx>:
Hello, I wanted to ask according such a problem which we had faced
with.
We are widely using postgres arrays like key->value array by doing
like
this:
{{1,5},{2,6},{3,7}}
where 1,2,3 are keys, and 5,6,7 are values. In our pgSql functions
we are
using self written array_input(array::numeric[], key::numeric)
function
which makes a loop on whole array and searches for key like
FOR i IN 1 .. size LOOP
if array[i][1] = key then
return array[i][2];
end if;
END LOOP;
But this was a good solution until our arrays and database had
grown. So
now
FOR loop takes a lot of time to find value of an array.
And my question is, how this problem of performance could be
solved? We
had
tried pgperl for string parsing, but it takes much more time than
our
current solution. Also we are thinking about self-written C++
function,
may
be someone had implemented this algorithm before?
you can use indexes or you can use hstore
Regards
Pavel Stehule
--
Best regards
Aleksej Trofimov
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It is strange - on my comp FOREACH is about 2x faster
postgres=# select input_value(array(select
generate_series(1,1000000)::numeric), 100000);
input_value
-------------
(1 row)
Time: 495.426 ms
postgres=# select input_value_fe(array(select
generate_series(1,1000000)::numeric), 100000);
input_value_fe
----------------
(1 row)
Time: 248.980 ms
Regards
Pavel
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--
Best regards
Aleksej Trofimov
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